Event sensor

ABSTRACT

An automatic timing measurement system that provides a measure of time of passage of a watercraft through a prescribed course. Algorithms based on inertial or other estimates augmented by GPS speed/position measurements are used to track position of a watercraft. Said position estimates are used to allow the locations of prescribed courses to be mapped and memorized. Algorithms are then used to allow the apparatus to automatically detect passage of a watercraft through mapped courses for the purpose of measuring and reporting time of passage of said watercraft past key points in said course, and for modifying the behavior of the speed control portion of the apparatus if necessary at certain points in the mapped course. A measure of accuracy of driver steering can be provided along with the ability to automatically steer the watercraft through the course if “steer-by-wire” mechanism is available. GPS speed control is augmented with a secondary velocity measurement device that measures speed over water resulting in an optional user selectable real-time compensation for water current. Furthermore, GPS is used as the key input to produce boat speed-based pull-up profiles.

This patent is a continuation-in-part patent application that claimspriority and incorporates herein by reference U.S. patent applicationSer. No. 11/056,848, now issued as U.S. Pat. No. 7,229,330; U.S. patentapplication Ser. No. 11/811,616, filed Jun. 11, 2007; U.S. patentapplication Ser. No. 11/811,605 filed Jun. 11, 2007; U.S. patentapplication Ser. No. 11/611,606, filed Jun. 11, 2007; U.S. patentapplication Ser. No. 11/811,604, filed Jun. 11, 2007; and U.S. patentapplication Ser. No. 11/811,617. filed Jun. 11, 2007.

FIELD OF THE INVENTION

The present invention pertains to the field of water sports and boatingand more specifically to electronic devices for use in water sports.

BACKGROUND OF THE INVENTION

Competitors in trick, jump, and slalom ski and wakeboard events requiretow boats capable of consistent and accurate speed control. Successfulcompletion of slalom and jump runs require passes through a competitionwater course at a precise specific speed. Competition rules usuallyrequire that said speed requirements be confirmed by use of a speedmeasurement system. For example, American Water Ski AssociationThree-Event Slalom and Jump competitions specify a required time windowfor completion of all segments of the course to confirm that speed wasmaintained adequately throughout the pass. These times have historicallybeen measured either using manual stopwatch measurements or, morerecently, using magnetic sensors which are triggered by the presence ofmagnets attached to buoys in the water in close proximity to the path ofthe tow boat at the required timing measurement points in the course.Course times have to be reported and logged for every individual pass incompetition. Reliability of triggering the magnetic sensor, as well asmaintenance of the magnets attached to the buoys has consistently causedmajor difficulties in running competitive 3-event competitions.

SUMMARY OF THE INVENTION

The present invention provides a consistent, maintenance free andaccurate method of measuring time of passage of a tow boat and skierthrough courses such as those used for slalom and jump competitionswithout the need for magnets or other physical attachments to the courseinfrastructure. Global Positioning System (GPS) satellite technology isused to map and memorize the location of courses in a permanent memorywithin a computer system. The system is then able to recognize everytime the tow boat passes through the course using continuously updatedGPS position estimates. By interpolating between periodic positionupdates, the system can accurately estimate time of closest approach tothe entry gate to the course, and subsequently track time to all pointsof interest down the course using either the same GPS positionmeasurement technique, or by tracking displacement of the tow boat downthe line of the course using other techniques such as integration ofvelocity to derive position displacement.

An automatic timing measurement system that provides a measure of timeof passage of a watercraft through a prescribed course. Algorithms basedon inertial or other estimates augmented by GPS speed/positionmeasurements are used to track position of a watercraft. Said positionestimates are used to allow the locations of prescribed courses to bemapped and memorized. Algorithms are then used to allow the apparatus toautomatically detect passage of a watercraft through mapped courses forthe purpose of measuring and reporting time of passage of saidwatercraft past key points in said course, and for modifying thebehavior of the speed control portion of the apparatus if necessary atcertain points in the mapped course. A measure of accuracy of driversteering can be provided along with the ability to automatically steerthe watercraft through the course if “steer-by-wire” mechanism isavailable. GPS speed control is augmented with a secondary velocitymeasurement device that measures speed over water resulting in anoptional user selectable real-time compensation for water current.Furthermore, GPS is used as the key input to produce boat speed-basedpull-up profiles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of external housing of thedevice of the instant invention.

FIG. 2 is a block diagram of the electronics contained within thehousing of FIG. 1.

FIG. 3 is a feedback control loop diagram demonstrating the operation ofan observer in accordance with a preferred embodiment of the presentinvention.

FIG. 4 is a diagram of an example water body including three skicourses.

FIG. 5 is a flow diagram disclosing a method that an observer inaccordance with a preferred embodiment of the present invention may useto determine observed velocity and observed position.

FIG. 6 is a flow diagram disclosing a method for automatically detectinga previously-mapped course.

FIG. 7 is a flow diagram disclosing a method of detecting and reportingthe time at which a plurality of events is detected.

FIG. 8 is a flow diagram disclosing a method by which a userinteractively “maps” a desired water course, and by which the presentinvention stores the mapped water course into non-volatile memory.

FIG. 9 is an example of a competitive slalom ski course.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates generally to electronic event detectorsand more specifically to electronic event detectors for use with powerboats.

As show in FIG. 1, the event detector 100 of the present inventionincludes a housing 102 for housing the electronics of the inventdetector an accelerometer 106 and a GPS 104. GPS 104 is preferably aunit separate from housing 102, e.g. a GARMIN® GPS18-5 Hz.

Electronic housing 102 includes a display 108 and interface buttons 110.As will be appreciated by one skilled in the art the display 108 ispreferably made out of moldable materials such as plastic, aluminum,glass, and the like, with a clear glass or plastic cover. Importantly,the housing is adapted to be waterproof to prevent damage to theelectronics when in use. The display 108 may be a commercially availableLCD display that is capable of displaying numbers or letters andinformation related to the event. User interface buttons 110 areactuators attached to the electronics covered in a rubberized membranethat allows buttons to remain waterproof during their actuation. The LCDdisplay interface buttons 110 and glass cover are attached to aninsulated housing 102 via e.g., screws, friction fit, adhesive, or thelike inside the housing 102 are electronics, to be described below, thatperform the functions of the device.

The electronics will now be described with reference to FIG. 2. Ingeneral, the electronics of the event locator device 100 includesmicroprocessor 200, non-volatile storage 202, GPS interface 204, Clock206, speaker 208, power device 210, user input interface 214,accelerometer 216, and analog-to-digital converter 218.

Microprocessor 200 is the “brains” of the invention and performslocation calculations and timing data for output to a user. Preferablymicroprocessor 200 is capable of being externally programmed. Volatilestorage 202 is connected to microprocessor 200 and stores event datasuch as map information, location information, and timing informationfor the microprocessor's calculations. Clock device 206 provides timedata to the microprocessor 200 which can be displayed to a user. GPSinterface 204 interfaces with the GPS system which provides locationdata to the microprocessor 200. Accelerometer 216 generates anacceleration signal and provides the same to the microprocessor 2000.AC/DC converter converts the signal from the accelerometer to a digitalsignal for input into the microcontroller 200. User input interface 214is connected to the microprocessor and allows the user to programcertain device settings into the non-volatile storage 202 such as mapinformation, desired speed, and the like. Display 212 interacts withmicroprocessor to display event data speed, location and timeinformation. Power supply 210 provides power to microcontroller and allof the associated electronics.

The general operation of microprocessor 200 will now be described inmore detail with reference to FIG. 3. Note FIG. 3 contemplates ascenario where course mapping information is already saved in memory andaccessible by the microprocessor. As is shown, the accelerometerreceives a signal from the boat indicative of the boat's accelerationand inputs this signal to a microprocessor. The microprocessor convertsthe acceleration value into a velocity value in step 15 and in step 16receives both the velocity information from the accelerometer and thevelocity data from the GPS. As one skilled in the art will appreciatethe velocity from a GPS is not updated continuously, and the velocityinformation from the accelerometer is used to provide resolution to thevelocity information from the GPS system in step 17. An observedvelocity is output at step 17, and in step 70 the velocity informationand direction information obtained from the GPS system is used tocalculate a latitude and longitude value for the accelerometer. In step80, latitude and longitude information from the GPS system is comparedto latitude and longitude information from the accelerometer. Much likestep 17, the latitude and longitude information from the accelerometeris then used to attenuate the GPS signal. The microprocessor thenoutputs a latitude and longitude observed signal, which is used inreference to map data input by the user at the start of the process.When a preselected event occurs, as calculated by the comparisonobserved latitude/longitude signals the microprocessor outputs a soundsignal to speaker 208 and a display signal to user display 108.

Collectively, the accelerometer 216, analog-to-digital converter 218,computing device 200, GPS unit 204, memory 221 and clock 206 comprisethe elements of an observer 222. The observer 222 is adapted to act bothas a velocity observer (in which it outputs an observed velocity) and asa position observer (in which it outputs an observed position). In thepreferred embodiment of the present invention, an accelerometer acts asthe primary source of data for computing displacements over time, withperiodic updates from the GPS provided to account for drift in theaccelerometer. But it will be appreciated by those skilled in the artthat there are many other methods available for performing this task.For example, over-water velocity may be measured directly by means of atransducer such as a paddle wheel or a pitot tube, and thosemeasurements may or may not be corrected with GPS inputs. In the case ofdirect velocity measurement, only a single integration with respect totime is needed to compute a new position. And, as GPS technology becomesmore accurate and as new data are available at a higher frequency, it isconceivable that a GPS unit will provide the sole velocity and positioninputs. Other configurations for measuring velocity and position will beapparent to those of ordinary skill in the art, and it is intended forthis patent to encompass such additional configurations.

The specific software flow of the microprocessor programming will bedescribed with reference to FIGS. 5 through 8.

FIG. 5 discloses the functioning of a preferred embodiment of anobserver 222. In step 501, a GPS signal is received from the GPS device204. GPS device 204 provides a GPS position 513, a GPS velocity 512, anda GPS direction 511. Step 501 uses the GPS position as its initialstarting position. In Step 502, there is a check to see if a new GPSposition has been received. If a new GPS position has been received, inStep 503 it is checked to see if the GPS position is a valid GPSposition. Step 503 compensates for the potential of invalid GPS signalssuch as occasionally occur in GPS devices known in the art. If the newGPS signal is a valid signal, then the observed position 509 is set to avalue of the accelerometer corrected by the difference between the lastobserved position and the GPS position 513. A constant 515 is providedsuch as is calculated to provide the appropriate weight to the GPSmeasurement. For example, if constant 515 is set to one, then the GPSposition is afforded its full weight. If constant 515 is set to a valueless than one, the GPS is provided less weight, and it if it set to avalue greater than one, the GPS is provided more weight. This constantis selected in accordance with the relative accuracies of the GPS andaccelerometer such that for a more accurate GPS device, greater weightcan be given to the GPS value and for a less accurate GPS device, lessweight can be given to the GPS value. The result of this calculation isan observed position 509.

It is necessary to compensate for the 5 Hz resolution of the GPS device.This resolution is insufficient for the preferred embodiment of thepresent invention. So there is provided an alternative device, startingat step 505, which includes an accelerometer 316. The accelerometerprovides a measured acceleration which is converted to a binary value inanalog-to-digital converter 218. It is then useful for being compared todigital values provided by the GPS device 204. In step 506, an observedvelocity is computed. The velocity is computed by first taking the lastobserved velocity 510 and the velocity provided by the GPS 512. Thisdifference is adjusted by a velocity constant 517. As with positionconstant 515, velocity constant 517 is selected to compensate for therelative accuracy of the GPS device. The weighted difference is thenadded to the velocity computed by taking the first integral of theacceleration with respect to time, thereby providing a correctionfactor. In step 507, an accelerometer-computed position 514 iscalculated. This position is computed by taking the integral of thevelocity vector with respect to time. The displacement calculatedthereby is adjusted to the direction signal provided by the GPS. ThisGPS correction step is used in the preferred embodiment because, in theinterest of simplicity, the three-accelerometer is used only to computeacceleration along the single axis of the length of the boat. The resultis accelerometer-computed position 514. The usefulness ofaccelerometer-computed position 514 is that it can be calculated at afrequency of approximately 1,000 hertz. So returning to step 502, if nonew GPS signal has been provided, then the observed position is providedby the change in position as calculated by the accelerometer with nofurther input from the GPS device. Thus, there is provided from theobserver an observed position 509 as well as an observed velocity 510.

FIG. 8 discloses a method of using a watercraft equipped with a positionand velocity observer, such as is described in FIG. 5, to map acompetitive water course. In step 801, there is initial determination ofthe position and velocity of the watercraft as provided by the observedvelocity 510 and the observed position 509. In step 802, there is acheck to see whether there has been a user input from a map button 214.If no user input is provided, then the position observer continuouslyupdates the position and velocity of the watercraft. Once there has beena user input at step 803, the current observed position 509 and thecurrent heading are stored in non-volatile storage 202. In step 805,there is provided a step of checking to see if it is desired to mapanother point. If another point is to be mapped, then there is a returnto step 801 and the method is repeated until, at step 805, there is nofurther point to mapped. When there is no further point to be mapped, atstep 806, the device may calculate a number of predeterminedintermediate points in between the points mapped and stored in step 803.These intermediate points are also stored in non-volatile storage 202.

In FIG. 6, there is disclosed a method of automatically detecting acourse that has been mapped in accordance with the method of FIG. 8. Atstep 601, there is initial determination of position and velocityprovided by observed position 509 and observed velocity 510. In step602, compare the observed position 509 to a predetermined position asmapped in accordance with the method of FIG. 8. This mapped position isprovided from non-volatile storage 202. In 603 there is a determinationof which of a plurality of mapped courses as mapped in accordance withthe method of FIG. 8 is the closest to the present observed position509. Once a closest course has been locked in, then, in step 604, thereis a check to see whether the watercraft is inside the lockout region ofthe closest water course. If the craft is within the lockout region,then there is also a check to see whether the craft is approaching fromoutside the course and is proceeding in the right direction along thecenter line of the course. If these criteria are not met, then continuelooking for entrance into a course. If the criteria are met, then, instep 606, check to see whether the craft has crossed the plane of theentry gate of the course. If it has not, then return to step 602,continuing looking for entry to a course. If the criteria are met, thenthe craft has entered a mapped course and the course timing algorithmwill automatically begin in step 607. This provides an observed positionat the entry point 608.

In FIG. 7 there is disclosed a method for computing total time andintermediate times through a competitive water course. There is providedan observed position at the entry point 608 and there is also provided aclock signal 206. In step 701, the time at the entry point is recordedin temporary memory 221. In step 702, an observed position 509 isprovided and this provides the present position of the watercraft. Aplurality of points of interest are stored in non-volatile storage 202.In step 703, a point of interest is provided and there is a check to seeif the current observed position 509 exceeds the position of the pointof interest. If the present position 509 does not exceed the position ofthe point of interest, then the loop is continued until the presentobserved position exceeds the position of the point of interest. At thispoint, in step 704, the present observed time 709 is recorded intotemporary memory 221 and, in step 705, the current observed time 709 isdisplayed on user display 212. In step 706, there is provided an idealtime 710. An error time 711 is computed as the difference between theideal time 710 and the observed time 709. The error time 711 is alsostored in temporary storage 221 and displayed on user display 212.

In a parallel process to step 704, when a point of interest is reached,there is also provided an audible signal through a speaker 208 toprovide an audible indication to the user that this point has beenpassed. After steps 704, 705, 706 and 708 are completed, then in step707 there is a check to see if this is the last point of interest. If itis not, then there is a return to step 702. If this is the last point ofinterest, the process ends.

The use of the device will now be described with respect to FIGS. 3, 4and 9.

As diagrammed in FIG. 3 showing feedback system 310, the inertiameasurement device (accelerometer) 216 measures the actual accelerationa_(a) of a watercraft 50 and the GPS device 204 measures the actualvelocity v_(a) and position of the same watercraft 50. The output fromthe accelerometer a_(Acc) is input into a first step 15 that covertsa_(Acc) to velocity v_(Acc). The output from first step 15 v_(Acc) andthe GPS output v_(GPS) are input to a second step 17. The output from asecond step 17 v_(OBS) and the output (Dir_(GPS)) indicating course ordirection of travel from the GPS device 204 are input into a third step70 to derive inertial-based estimates of the latitude (Lat_(Acc)) andlongitude (Long_(Acc)) of the watercraft 50. Direct GPS measurements oflatitude (Lat_(GPS)) and longitude (Long_(GPS)) and the outputs from thethird step 70 are input in a fourth step 80 to correct inertial-basedestimates of the latitude (Lat_(Acc)) and longitude (Long_(Acc)) of thewatercraft 50 to account for any inaccuracies due to drift oracceleration sensor inaccuracies. Lat_(OBS) and Long_(OBS) can then beused to allow the boat driver to record via a user interface theabsolute latitude and longitude position coordinates of a course to besaved into a permanent non-volatile memory. Coordinates can be recordedeither by direct numerical entry of measured coordinates, or bysnapshotting course coordinates as the boat is maneuvering through thecourse to be mapped. The driver can identify course reference points viaa user interface (not shown) or button press as the boat passes thepoint to be mapped. Since all courses of interest are laid out instraight lines, mapping of two known points in a course is sufficient tofully define the locations of all points of interest in a course andit's direction relative to earth latitude and longitude coordinates. Allfuture passages of the towboat within a specified distance of selectedcourse coordinates as measured by Lat_(OBS) and Long_(OBS) can then bedetected and used to initiate timing measurements of the towboat throughthe mapped course.

FIG. 9 discloses a competitive slalom ski course. This is the type ofcourse on which an embodiment of the present invention may be used.There is shown an entry gate 901, which can be characterized by aprecise global coordinate specified in latitude and longitude. Theopposite end point of the course is exit gate 905, which may also becharacterized as a latitude and longitude. Because the course lies alonga substantially straight line, the locations of all points of interestalong the course can be found given the positions of the two end points.A course centerline 906 lies along a substantially straight line and isslightly larger than the width of a water craft. The centerline isdefined by boat buoys 904, which the water craft must stay in between.There are also provided ski buoys 902, which the skier must ski aroundduring the passage of the course, in an alternating pattern as shown bythe ski path 903. The skier must pass between the buoys defining firstbreak point 907 before proceeding along ski path 903. At the end of thecourse is a second break point 908. The skier must ski between the twobuoys defining second break point 908 after passing around the last buoy902. In between these points are six intermediate points 904, eachdefined by a pair of buoys, which are positioned to be substantiallycollinear with the ski buoys 902.

The entry gate 901, exit gate 905, break points 907 and 908 andintermediate buoys 904 are all points of interest whose passage may needto be detected. The time at which the boat 50 passes these points may beused to determine whether a run is valid, according to whether the timeis within an allowable margin of error. Because these points are definedaccording to precisely-surveyed distances, their locations can bedetected by a substantially accurate observer (such as is provided bythe preferred embodiment of the present invention) given only thelocation of the two end points. So the mapping course-mapping methoddescribed in FIG. 8 provides the observer with sufficient information todetermine when a point of interest has been passed in accordance withthe method of FIG. 7.

Once a course has been mapped, the location of the course can be storedin a permanent storage medium 202 such as a disk drive or flash memory.Further qualification of valid entry to a course can then be carried outbased on GPS direction measurements so that timing measurements are onlymade when the towboat enters a mapped course while traveling along theknown direction of the course centerline. Further, any deviations of thetow boat from the center line of the course can be detected and factoredgeometrically into the measurement of displacement down the centerlineof the course so that errors in timing measurement due to driversteering error can be compensated for.

FIG. 4 discloses a water course with a plurality of competitive skicourses. There is disclosed a first slalom course 401, a second slalomcourse 402 and a jump course 403. First slalom course 401 has entry andexit thresholds 405. Second slalom course 402 has entry and exitthresholds 406. The slalom courses may be traversed in either directionthrough entry and exit thresholds 405 and 406. A jump course 403 may beentered only through entry threshold 411 because ski jump 409 isunidirectional.

According to a preferred embodiment of the present invention, a user mayapproach a course, for example first slalom course 401. Upon enteringthe entry threshold 405 in the direction of the course centerline 408,the user will press a button whereby the computing device is alerted ofthe location of the entry/exit threshold. The user then proceeds alongcourse centerline 408 and presses a button again at the oppositeentry/exit threshold 405.

The computing device also interfaces with a permanent storage medium.This storage medium contains the desired locations of intermediate buoys407, which are located at pre-determined distances from the entry/exitbuoys. “This process” allows the computing device to learn the exactlocation of first slalom course 401. “The process” can then be repeatedto allow the computing device to learn the locations of second slalomcourse 402 and jump course 409.

Once the computing device has learned the locations of courses 401, 402and 403, it is desirable for the device to automatically detect whichcourse it is at without further user intervention. So there are shownmapped lockout regions 404 around each of the entry/exit thresholds 405,406 and 411. According to the method disclosed in FIG. 6, the devicewill detect which of the mapped courses is closest to its presentposition. The device may also selectively detect only courses of aspecific type (jump or slalom) depending on its current mode ofoperation. If the device then determines it is within a lockout regions404, it will check to see if the boat is approaching from outside theentry/exit threshold and in the correct direction along the coursecenterline. If these criteria are met, then the device will calculatethe time o the closest approach to the plane of the entry gate. At thattime it will begin timing the path without any intervention from theuser.

Because the locations of intermediate buoys 407 are pre-programmed, thedevice may provide an audible or visual indication of the passing ofeach intermediate buoy 407. It may also provide intermediate times atthe passing of each intermediate buoy 407. Finally, it will calculatethe time at which boat 50 passes through the opposite entry/exitthreshold 405.

In this manner the device can automatically time a pass through amemorized course without any further intervention from the user.

A driver score can also be provided based on the degree of this errorwhich can be used to rate driver performance and confirm accuracy of theboat path through the course, which is also a criterion used in judgingwhether a competitive pass is valid.

Any boat speed or engine torque modification requirements which maydepend on position in the course can be triggered based on Lat_(OBS) andLong_(OBS) relative to the mapped course location.

As one skilled in the art will recognize, the device of the invention isone of the category of commonly understood instruments that measures anobject's acceleration. The velocity of on object can be calculated byintegrating the acceleration of an object over time. Further, theposition of an object relative to a known starting point can becalculated by integrating the velocity of an object over time. A GPSdevice is one of the category of commonly understood instruments thatuse satellites to determine the substantially precise global positionand velocity of an object. Such position and velocity measurements canbe used in conjunction with timers to determine an object'sinstantaneous velocity and average velocity between two points, alongwith its absolute position at any point in time. A comparator is anyanalog or digital electrical, electronic, mechanical, hydraulic, orfluidic device capable of determining the sum of or difference betweentwo input parameters, or the value of an input relative to apredetermined standard. An algorithm is any analog or digitalelectrical, electronic, mechanical, hydraulic, or fluidic device capableof performing a computational process. The algorithms disclosed hereincan be performed on any number of computing devices commonly calledmicroprocessors or microcontrollers, examples of which include theMotorola® MPC555 and the Texas Instruments® TMS320

Use of observed velocity and position estimates based on inertial orother measurement sources allows for error correction of occasionalglitches or interruptions in availability of accurate GPS velocity andposition measurements. These can occur in the course of normaloperations, either due to GPS antenna malfunction, or temporary loss ofGPS satellite visibility due to overhead obstruction from bridges oroverhanging vegetation and the like.

Other embodiments of the system could include automated steering of theboat down the centerline of the course making use of course locationinformation stored as described in 0014 thru 0016 above. The presentinvention may be included as part of an electronic closed-loop feedbacksystem that controls the actual angular velocity ωa of a boat propeller,and, indirectly, the actual over land velocity V_(a) of the watercraftpropelled by that propeller.

Another embodiment allows the apparatus to track the position of a skierbehind the watercraft as he/she traverses the course. This can beachieved by mounting a GPS antenna somewhere on or near the body of theskier and capturing these data concurrently with data from a tow boatmounted antenna. Such GPS antennae can be either wired or wirelesslyconnected to the main apparatus.

It will be apparent to those with ordinary skill in the relevant arthaving the benefit of this disclosure that the present inventionprovides an apparatus for tracking the position and velocity of awatercraft through a prescribed course without the need for measurementaids such as magnets built into the course infrastructure. It isunderstood that the forms of the invention shown and described in thedetailed description and the drawings are to be taken merely aspresently preferred examples and that the invention is limited only bythe language of the claims. The drawings and detailed descriptionpresented herein are not intended to limit the invention to theparticular embodiments disclosed. While the present invention has beendescribed in terms of one preferred embodiment and a few variationsthereof, it will be apparent to those skilled in the art that form anddetail modifications can be made to that embodiment without departingfrom the spirit or scope of the invention.

1. A system for detecting the time of an event, said system comprising:a position observer subsystem; a computing device in communication withsaid position observer system; non-volatile storage programmed withlocational information describing at least one water course; whereinsaid computing device is adapted to compute a position of a watercraftrelative to said water.
 2. The system of claim 1 further comprising Auser interface allowing driver inputs to permanently store and identifylocations of a prescribed course using measurements derived by 1 above.3. The system of claim 2 wherein said user interface further comprises aprogress indicator adapted to substantially represent said watercraftsposition relative to said mapped water course.
 4. The system of claim 2wherein said user interface is further adapted to provide an audiblesignal when said watercraft crosses the plane of a buoy.
 5. The systemof claim 1 wherein said computing device is adapted to automaticallydetect passage of said watercraft through defined points in said course.6. The system of claim 1 wherein said permanent storage medium containsa plurality of mapped water courses; and wherein said computing deviceis adapted to automatically detect which of said plurality of mappedwater courses said watercraft is entering.
 7. The system of claim 1wherein said computing device is adapted to measure driver accuracy insteering said watercraft through said mapped water course.
 8. The systemof claim 1 wherein said computing device is adapted to automaticallycompute a desired path through a mapped course; and further comprising acontrol system adapted to steer said watercraft along an actual pathsubstantially in conformance with said desired path.
 9. The system ofclaim 1 further comprising A computing device adapted to map and displaythe track of a skier relative to the course location in real time. 10.The system of claim 1 further comprising An algorithm adapted to map andlog the track of a skier relative to the course location based onpost-processing data.
 11. An apparatus for measuring the position of awatercraft, said apparatus comprising: a GPS device capable of computinga substantially correct position of said water craft; a permanentstorage medium containing locational information for at least onememorized water course; wherein said GPS device is adapted to calculatea position of said watercraft relative to said at least one memorizedwater course.
 12. A method of detecting an event comprising the stepsof: recording map data into a memory; receiving a velocity signal and alocation signal; outputting a normalized signal based upon said velocitysignal and said location signal; comparing said normalized to said mapdata; outputting said even based upon said comparison.